1. Field of the Invention
This invention relates in general to shoes and more specifically to shoes having articulated soles.
2. Description of the Prior Art
Many present day shoes, including a large number of running shoes, do not easily bend longitudinally at the region of the ball of the foot. Adverse consequences are common when such shoes are worn for the purpose of athletic participation or extensive walking. Some common consequences are: (a) strain of the anterior leg, ankle or foot structures; (b) increased likelihood of ankle sprain; (c) over use of posterior leg muscles or tendons; (d) excessive pronation if the leg is weak or tired; (e) heel strain, including heel spurs; and (f) pulling or slipping of shoe on rear part of foot.
Furthermore, some present day shoes are as stiff as a board at the bottom in the region extending from the back of the heel to the metartarsus. If the heel of the shoe is not rounded on the bottom, there is a tendency for the shoe and foot to slap down hard upon heel strike. In consequence, extensive walking or athletic participation may cause strains of the anterior leg, ankle, or foot structures. If on the other hand, the heel of the shoe is adequately rounded to prevent such strain, then calf strain, achilles tendon strain, or heel strain is likely.
Inflexibility as described above is sometimes avoided by making the sole thin or by constructing the sole out of very flexible materials. A common failing of such shoes is that they lack stability. Another failing, most apparent in running shoes, is that if longitudinal flexibility at the ball is good, then shock absorption in that region is unsatisfactory.
It is known to those of ordinary skill in the art that some outer soles have transverse ripples which extend across the ball of the foot for longitudinal flexibility. Such ripples frequently wear rapidly and cannot be maintained conveniently by present methods.
A new outer sole manufactured by the Adidas Company is employed on running shoes identified as models "SL-80" and "Runner Super". That sole is articulated along curved lines in the ball and heel regions. The articulations do not protrude into the midsole of the shoe. The construction principally provides longitudinal sole flexibility under the toes well forward of the ball of the foot.
Several shoes of particular interest are described in the patent literature. In U.S. Pat. No. 3,507,057 issued to Olof Goete Olssen, a wooden shoe having a V-shaped transverse hinge joint situated "directly rearwardly of the ball of the foot" is disclosed. U.S. Pat. No. 4,130,947, issued to Francis Denu, discloses an athletic shoe having a sole comprised of an upper layer and a lower layer. The upper surface of the lower layer conforms to the downwardly projecting transverse ribs of the upper layer. In U.S. Pat. No. 4,030,213 the inventor, Alexander C. Daswick, discloses a sport shoe having a transverse joint located in the region of the shank thereof.
Efforts have been made to improve the flexibility of spiked sport shoes. Methods of possible interest are disclosed in U.S. Pat. No. 3,127,687, issued to Solomon C. Hollister, U.S. Pat. No. 3,341,952 issued to Adolf Dassler, and U.S. Pat. No. 3,487,563 issued to Clive J. Austin.
Two magazine articles of interest were written by Richard Schuster and appeared in the February, 1980 and March, 1980 editions of THE RUNNER. They are entitled respectively "Point of Purchase: 10 Points" and "Evolution of the Running Shoe".
Another feature of the present invention is the use of shank stiffeners in the context of an articulated shoe sole. An extensive history of the prior art that relates to shank stiffeners is presented in my copending application, Ser. No. 134,651 filed on Mar. 27, 1980. Further detailed discussion may be found in the Prior Art Statement filed with that application. The contents of the aforedescribed copending application and Prior Art Statement are hereby incorporated in total by reference into this application.